Pulsed high current technique for characterization of device under test

ABSTRACT

A test and measurement circuit including a capacitor in parallel with a device under test, a direct current voltage source configured to charge the capacitor, a pulse generator configured to generate a pulse for testing the device under test, and a sensor for determining a current in the device under test.

PRIORITY

This disclosure claims benefit of U.S. Provisional Application No.62/892,450, titled “PULSED HIGH CURRENT TECHNIQUE FOR CHARACTERIZATIONOF A DEVICE UNDER TEST,” filed on Aug. 27, 2019, which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

This disclosure is directed to systems and methods related to test andmeasurement systems, and in particular, to systems and methods forperforming device characterization of a device under test.

BACKGROUND

Device characterization, such as characterization of a semiconductordevice, e.g., a power Metal-Oxide-Semiconductor Field-Effect Transistor(MOSFET), may involve applying voltages to the terminals of the device,and measuring the resulting currents that flow through the device. Suchdevice characterization may include the generation of a plot of currentversus voltage called an UV curve or an I/V sweep.

Conventional systems and methods for characterizing a device under testgenerally rely on direct current (DC) sourcing instruments, such assource measure units (SMUs), to apply voltages to the device under testand perform measurements while voltages are applied. As the currentincreases, the DC voltages are applied over shorter time frames to limitpower dissipation in the device under test. However, such testingmethods run into measurement instrument power limitations at highcurrents, as well as device under test power dissipation limitations.Further, high current delivery can become very difficult through acabled system due to resistive losses and inductive voltage drops.

Embodiments of the disclosure address these and other deficiencies ofthe prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects, features and advantages of embodiments of the presentdisclosure will become apparent from the following description ofembodiments in reference to the appended drawings in which:

FIG. 1 is an example of a conventional measurement circuit forcharacterizing a device under test.

FIG. 2 is an example of a measurement circuit for characterizing adevice under test according to some embodiments of the disclosure.

FIGS. 3 and 4 are examples of a conventional current versus voltagecurve by a manufacturer of a device under test.

FIG. 5 is an example of a current versus voltage curve determined by themeasurement circuit of FIG. 1.

FIG. 6 is another example of a measurement circuit for characterizing adevice under test according to other embodiments of the disclosure.

FIG. 7 is another example of a measurement circuit for characterizing adevice under test according to other embodiments of the disclosure.

FIG. 8 is an example of alternative techniques for producing a currentversus voltage curve for characterizing a device under test according toother embodiments of the disclosure.

DESCRIPTION

FIG. 1 illustrates a conventional measurement circuit 100 forcharacterizing a device under test 102. In the circuit 100 of FIG. 1,the device under test 102 is a transistor. Voltage is applied to thedevice under test 102 at the gate by a DC voltage source 104 and at thedrain by another DC voltage source 106. The circuit 100 also includes asetup resistor 108 and a setup inductor 110. In some cases, theillustrated setup resistor 108 and setup inductor 110 can representparasitic elements of one or more components of the measurement circuit100. When the voltages are applied to the gate and drain of the deviceunder test 102, the current can be measured across the setup resistor108 to determine the characterizations of the device under test.However, as discussed above, the circuit 100 runs into instrument powerlimitations at high currents and due to this it can be difficult tocharacterize the device under test 102 at these high currents.

When high current characterization is needed, then the conventionalmeasurement circuit 100 becomes impractical. Resistive drop, inductivelimitation, power line limits, and device under test power dissipationall become difficult to overcome. Embodiments of the disclosure, asdiscussed in more detail below, can overcome these difficulties byplacing an energy storage device close to the device under test,optimizing circuit connections and layout to minimize series resistanceand inductance, using fast data acquisition over a required device undertest operating range, and letting the device under test set theoperating point and IV sweep.

FIG. 2 illustrates an example measurement circuit 200 according to someembodiments of the disclosure. The measurement circuit 200 forcharacterizing a device under test 202 includes a sensor 204 formeasuring drain current of the device under test 202. The sensor 204,may be, for example, a resistor and associated sensing circuitry. Themeasurement circuit 200 also includes a DC power supply 206 for charginga local capacitor 208. The DC power supply 206 may be included in a testand measurement instrument, such as a source measure unit, or may beincluded as a separate DC power supply. The measurement circuit 200 alsoincludes a pulse generator 210 and an inductor 212. In some embodiments,the illustrated inductor 212 can represent parasitic elements of one ormore components of the measurement circuit 200.

The local capacitor 208 is physically located near the device under test202, while the DC power supply 206 may be remote from the device undertest 202. The local capacitor 208 is charged by the DC power supply 206to a predetermined voltage. The predetermined voltage may be set at theDC power supply 206 by a user in some embodiments. The predeterminedvoltage can be the highest drain to source voltage (V_(DS)) that shouldbe tested or used across the drain to source of the device under test202.

When the local capacitor 208 is fully charged to the predeterminedvoltage, the pulse generator 210 generates a pulse at a specific orknown voltage which is received at the gate, or a similar controlterminal, of the device under test 202. When the gate of the deviceunder test 202 receives the pulse from the pulse generator 210, thedevice under test 202 discharges the energy stored in the localcapacitor 208. As the local capacitor 208 is discharging, a test andmeasurement instrument can measure the voltage and current relationshipin the device under test 202 by testing the current through the sensor204 as well as the voltage across the device under test 202. The testand measurement instrument can be any test and measurement instrumentthat can measure the current and voltage, including, but not limited to,a high-speed digitizing circuit or an oscilloscope.

The measurement circuit 200 of FIG. 2 can deliver, for example, a 20Volt to 50 Volt open circuit and 4000 Amperes to 10,000 Amperes of shortcircuit current. These voltage and current ranges are merely examples.Embodiments of the invention are not limited to these example ranges.The high current flow through the measurement circuit 200 is limited toa tight loop between the device under test 202, the local capacitor 208,and the sensor 204.

In some embodiments, the gate voltage can be pulsed with the pulse fromthe pulse generator 210 with respect to the source voltage to eliminategate voltage dependence on the device under test 202 current flow. Whenthe pulse is wide, the DC power supply 206 voltage will interact withthe drain current flow unless it floats with respect to measurementcircuit 200. In such a situation, the test and measurement instrumentwould need both the drain current and the current measured at the sensor204 to be measured to arrive at the correct current value.

In some embodiments, the sensor 204 may be located on the drain or HIside, rather than the source or LO side, of the device under test 202.

Due to the limited testing or characterization abilities of conventionaltest and measurement circuits, such as the measurement circuit 100 shownin FIG. 1, device under test manufacturers, such as semiconductormanufacturers, often are only able to provide a limited characterizationof the semiconductor devices, as illustrated in FIGS. 3 and 4. FIG. 3illustrates a set of IV curves 300 only up to 1.4 Volts for a drainsource voltage (V_(DS)) and 350 Amperes, while FIG. 4 illustrates a setof IV curves 400 up to 10 Volts for V_(DS) and 350 Amperes. Each curveof the set of IV curves 300 and 400 illustrates a different gate-sourcevoltage (V_(GS)) applied at the gate. The devices under test are noteasily able to be characterized at currents higher than 350 Amperesaccurately.

FIG. 5, however, illustrates an example of a set of IV curves 500obtained from characterizing a device under test by measurement circuit200. Using embodiments of the disclosure, the IV curves 500 can beobtained up to a much higher drain-source voltages (Vds), and muchhigher currents, such as the 1300 Amperes illustrated in the IV curves500 of FIG. 5. Each IV curve 502, 504, 506, 508 of the IV curves 500illustrates the response of the device under test 202 when differentvoltage pulses, e.g. pulses with different amplitudes, are generated bythe pulse generator 210. These voltage and current ranges are merelyexamples. Embodiments of the disclosure are not limited to these exampleranges.

According to some embodiments of the disclosure, an IV curve may begenerated using a piecemeal or segmented measurement technique, asdepicted in FIG. 8 for example. FIG. 8 illustrates three plots 810, 820,830 of signals 812, 822, 832, such as the voltage signal generated bypulse generator 210 of FIG. 2, which is received at a control terminalof a DUT, such as the gate of DUT 202 in FIG. 2. FIG. 8 also illustratesthree plots 815, 825, 835 that correspond to plots 810, 820, 830,respectively. Plot 815 shows an IV curve 817 that is measured inresponse to the control terminal pulse 812 shown in plot 810. Asdiscussed above, the pulse 812 causes the DUT 202 to turn on, andcurrent through the DUT is measured as the capacitor 208 of FIG. 2discharges. Thus, the IV curve 817 may be continuously measured andgenerated in time from high V_(DS) to low V_(DS) as shown by the “time”arrow in plot 815.

In contrast, in plots 820 and 830 of FIG. 8, the control terminal pulses822 a-822 d and 832 a-832 d are much narrower, and may have a delay 824,834 between each pulse. Each of the narrow pulses 822 a-822 d may beused to measure and generate a segment A-D of IV curve 827 in plot 825.For example, pulse 822 a causes current to flow in the DUT 202, whichmay be measured as the capacitor 208 discharges, and used to generatesegment 829 a of IV curve 827. At the end of pulse 822 a, the DUT turnsoff, stopping the current flow. The next pulse 822 b again causescurrent to flow in the DUT 202, which maybe measured as capacitor 208discharges further, and used to generate segment 829 b of IV curve 827.Likewise, IV curve segment 829 c corresponds to pulse 822 c, and segment829 d corresponds to pulse 822 d. Within each segment 829 a-829 d of theIV curve 827, the current through the DUT is measured in time from highV_(DS) to low V_(DS) as shown by the “time” arrow in plot 825. Plots 830and 835 depict an alternative embodiment of a segmented technique forgenerating IV curves. The pulses 832 a-832 d and delays 834 in plot 830are similar to the pulses 822 a-822 d and delays 824 in plot 820.However, in this embodiment, the supply voltage to the DUT, such as thesignal from DC power supply 206 in FIG. 2, can be made to be anincreasing voltage ramp. Typically, this would be a slowly increasingramp. Thus, in this embodiment, pulse 832 a of plot 830 corresponds tomeasurement of segment 839 a of IV curve 837. Likewise, pulse 832 bcorresponds to measurement of segment 832 b, pulse 832 c corresponds tosegment 839 c, and pulse 832 d corresponds to segment 839 d. Thisembodiment allows the IV curve segments 839 a-839 d to be generated inorder from the lower V_(DS) segment 839 a to the higher V_(DS) segment839 d. However, within each segment 839 a-839 d of the IV curve 837, thecurrent through the DUT is still measured in time from high V_(DS) tolow V_(DS) as shown by the multiple “time” arrows in plot 835.

Although the description above uses the example of a MOSFET as thedevice under test 202, embodiments of the disclosure may be used tocharacterize many other types of devices, including all types oftransistors. Moreover, the device under test 202 of embodiments of thedisclosure are also not limited to three-terminal devices liketransistors, and other types of devices under test 202 may also betested using a measurement circuit according to embodiments of thedisclosure.

FIG. 6, for example, illustrates a measurement circuit 600 for measuringa two-terminal device under test 602. The measurement circuit 600includes, similar to measurement circuit 200, a sensor 604, a DC powersupply 606, a local capacitor 608, a pulse generator 610, and aninductor 612. Since the measurement circuit 600 is used for measuring atwo-terminal device under test 602, such as a diode, a three-terminalswitch 614 may be used to facilitate the characterization or testing ofthe device under test 602.

In the measurement circuit 600 of FIG. 6, the switch 614 is located inseries with the device under test 602 on the low side of the deviceunder test 602. However, the switch 602 could be located in series withthe device under test 602 on the high side of the device under test 602in some embodiments.

Similar to the measurement circuit 200 of FIG. 2, a pulse is generatedat a particular voltage at the pulse generator 602 to the gate, orcontrol terminal, of the switch 614. As the switch 614 turns on with thepulse, the local capacitor 608 is discharged and current flows throughthe device under test 602. The current flowing through the device undertest 602 can be measured at the sensor 604 while the voltage is measuredacross the device under test 602. Both the current and the voltage canbe measured by a test and measurement instrument, such as a high-speeddigitizing circuit or an oscilloscope.

The measured current of the device under test 602 may be used to providea current limit or an additional regulating device could be used to seta constant voltage or current for a limited time. The limited time canbe determined by the local capacitor 608. That is, a current limiter maybe added to circuits 200 or 600 to limit the current through the DUT,based on the maximum current the DUT can handle. The maximum DUT currentmay be entered by a user though a user interface, or may be known from aDUT manufacturer's data sheet. Furthermore, in order for the instrumentto test a variety of DUTs with a wide range of maximum currents,circuits 200 or 600 may include a switchable bank of energy storagedevices, such as capacitors 208, 608, that may be switched in dependingon the maximum current capacity of the DUT.

FIG. 7 illustrates a measurement circuit 700, which employs a switch714, similar to switch 614 in measurement circuit 600, but which may beused to characterize a three-terminal DUT 702, like circuit 200. Thecurrent sensor 704, DC power supply 706, capacitor 708, pulse generator710, and inductor 712 are similar to the current sensor 604, DC powersupply 606, capacitor 608, pulse generator 610, and inductor 612 of FIG.6. Like switch 614, switch 714 receives a pulse control signal frompulse generator 710 to turn the switch on, and cause current to flow inthe DUT 702. However, the DUT 702 in FIG. 7 is a three-terminal device,such as a transistor. Measurement circuit 700 also includes a voltagesource 716 coupled to the DUT. The voltage source 716 may be used to seta bias voltage of the DUT 702. The bias voltage may either be a DClevel, or may also be a pulse, which can be synchronized with the pulsefrom pulse generator 710. In still other embodiments, the functionalityof pulse generator 710 and the voltage source 716 may be swapped. Theswitch 714 may provide additional control of the test conditions, suchas enabling the drain voltage of the device under test while the gatevoltage is present on the device under test.

The measurement circuits shown in FIGS. 2, 6 and 7 can be included in asingle device or package, including the DC voltage sources 206, 606, 706and connect directly to the devices under test 202, 602, 702. That is,the measurement circuit will be physically close to the device undertest. In other embodiments, the DC voltage sources 206, 606, 706 may bea distance away from the device under test. However, in each embodiment,the capacitors 208, 608, 708 are each provided physically close to thedevices under test 202, 602, 702 to minimize series resistance andinductance.

Aspects of the disclosure may operate on particularly created hardware,firmware, digital signal processors, or on a specially programmedcomputer including a processor operating according to programmedinstructions. The terms controller or processor as used herein areintended to include microprocessors, microcomputers, ApplicationSpecific Integrated Circuits (ASICs), and dedicated hardwarecontrollers. One or more aspects of the disclosure may be embodied incomputer-usable data and computer-executable instructions, such as inone or more program modules, executed by one or more computers(including monitoring modules), or other devices. Generally, programmodules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types when executed by a processor in a computer or otherdevice. The computer executable instructions may be stored on a computerreadable storage medium such as a hard disk, optical disk, removablestorage media, solid state memory, Random Access Memory (RAM), etc. Aswill be appreciated by one of skill in the art, the functionality of theprogram modules may be combined or distributed as desired in variousaspects. In addition, the functionality may be embodied in whole or inpart in firmware or hardware equivalents such as integrated circuits,FPGA, and the like. Particular data structures may be used to moreeffectively implement one or more aspects of the disclosure, and suchdata structures are contemplated within the scope of computer executableinstructions and computer-usable data described herein.

The disclosed aspects may be implemented, in some cases, in hardware,firmware, software, or any combination thereof. The disclosed aspectsmay also be implemented as instructions carried by or stored on one ormore or computer-readable storage media, which may be read and executedby one or more processors. Such instructions may be referred to as acomputer program product. Computer-readable media, as discussed herein,means any media that can be accessed by a computing device. By way ofexample, and not limitation, computer-readable media may comprisecomputer storage media and communication media.

Computer storage media means any medium that can be used to storecomputer-readable information. By way of example, and not limitation,computer storage media may include RAM, ROM, Electrically ErasableProgrammable Read-Only Memory (EEPROM), flash memory or other memorytechnology, Compact Disc Read Only Memory (CD-ROM), Digital Video Disc(DVD), or other optical disk storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, and any othervolatile or nonvolatile, removable or non-removable media implemented inany technology. Computer storage media excludes signals per se andtransitory forms of signal transmission.

Communication media means any media that can be used for thecommunication of computer-readable information. By way of example, andnot limitation, communication media may include coaxial cables,fiber-optic cables, air, or any other media suitable for thecommunication of electrical, optical, Radio Frequency (RF), infrared,acoustic or other types of signals.

EXAMPLES

Illustrative examples of the technologies disclosed herein are providedbelow. An embodiment of the technologies may include any one or more,and any combination of, the examples described below.

Example 1 is a test and measurement circuit, comprising a capacitor inparallel with a device under test; a direct current voltage sourceconfigured to charge the capacitor; a pulse generator configured togenerate a pulse for testing the device under test; and a sensor fordetermining a current in the device under test.

Example 2 is the test and measurement circuit of Example 1, wherein thecapacitor discharges when the pulse causes the current to flow in thedevice under test and the sensor determines the current in the deviceunder test as the capacitor discharges.

Example 3 is the test and measurement circuit of either Example 1 or 2,wherein the pulse generator is configured to generate the pulse at apredetermined voltage.

Example 4 is the test and measurement circuit of any of Examples 1 to 3,wherein the direct current voltage source charges the capacitor to apredetermined level based on the device under test.

Example 5 is the test and measurement circuit of any of Examples 1 to 4,wherein the pulse is received at a control terminal of the device undertest.

Example 6 is the test and measurement circuit of any of Examples 1 to 5,further comprising a switch, wherein the switch is configured to receivethe pulse from the pulse generator to discharge the capacitor.

Example 7 is the test and measurement circuit of Example 6, wherein thepulse is received at a control terminal of the switch.

Example 8 is the test and measurement circuit of any of Examples 1 to 7,wherein the sensor comprises a resistor.

Example 9 is a test and measurement instrument, comprising themeasurement circuit of any of Examples 1 to 8; and a measurement deviceconfigured to measure the current through the sensor.

Example 10 is the test and measurement instrument of Example 9, whereinthe measurement device is further configured to measure a voltage of thedevice under test simultaneously with measuring the current through thesensor, wherein the measured current through the sensor substantiallyrepresents the current in the device under test.

Example 11 is a method for characterizing a device under test,comprising charging a capacitor by a direct current voltage source;generating a pulse by a pulse generator for testing the device undertest; and measuring a current through the device under test based on thepulse.

Example 12 is the method of Example 11, wherein the capacitor dischargeswhen the pulse is received at the device under test and the methodfurther includes measuring the current through the device under test asthe capacitor discharges.

Example 13 is the method of Example 11 or 12, wherein the pulse isgenerated at a predetermined voltage.

Example 14 is the method of any of Examples 11 to 13, wherein the directcurrent voltage source charges the capacitor to a predetermined levelbased on the device under test.

Example 15 is the method of any of Examples 11 to 14, further comprisingreceiving the pulse at a control terminal of the device under test.

Example 16 is the method of any of Examples 11 to 15, further comprisingreceiving the pulse from the pulse generator at a switch to dischargethe capacitor.

Example 17 is the method of any of Examples 11 to 16, wherein the pulseis received at a control terminal of the switch.

Example 18 is the method of any of Examples 11 to 17, wherein thecurrent is measured using a resistor in series with the device undertest.

Example 19 is the method of any of Examples 11 to 18, wherein thecurrent is measured through the resistor as the capacitor discharges.

Example 20 is the method of Example 19, further comprising measuring avoltage of the device under test simultaneously with measuring thecurrent.

The previously described versions of the disclosed subject matter havemany advantages that were either described or would be apparent to aperson of ordinary skill. Even so, these advantages or features are notrequired in all versions of the disclosed apparatus, systems, ormethods.

Additionally, this written description makes reference to particularfeatures. It is to be understood that the disclosure in thisspecification includes all possible combinations of those particularfeatures. Where a particular feature is disclosed in the context of aparticular aspect or example, that feature can also be used, to theextent possible, in the context of other aspects and examples.

Also, when reference is made in this application to a method having twoor more defined steps or operations, the defined steps or operations canbe carried out in any order or simultaneously, unless the contextexcludes those possibilities.

Although specific examples of the invention have been illustrated anddescribed for purposes of illustration, it will be understood thatvarious modifications may be made without departing from the spirit andscope of the invention. Accordingly, the invention should not be limitedexcept as by the appended claims.

We claim:
 1. A test and measurement circuit, comprising: a capacitor inparallel with a device under test; a direct current voltage sourceconfigured to charge the capacitor; a pulse generator configured togenerate a pulse for testing the device under test; and a sensor fordetermining a current in the device under test.
 2. The test andmeasurement circuit of claim 1, wherein the capacitor discharges whenthe pulse causes the current to flow in the device under test and thesensor determines the current in the device under test as the capacitordischarges.
 3. The test and measurement circuit of claim 1, wherein thepulse generator is configured to generate the pulse at a predeterminedvoltage.
 4. The test and measurement circuit of claim 1, wherein thedirect current voltage source charges the capacitor to a predeterminedlevel based on the device under test.
 5. The test and measurementcircuit of claim 1, wherein the pulse is received at a control terminalof the device under test.
 6. The test and measurement circuit of claim1, further comprising a switch, wherein the switch is configured toreceive the pulse from the pulse generator to discharge the capacitor.7. The test and measurement circuit of claim 6, wherein the pulse isreceived at a control terminal of the switch.
 8. The test andmeasurement circuit of claim 1, wherein the sensor comprises a resistor.9. A test and measurement instrument, comprising: the measurementcircuit of claim 1; and a measurement device configured to measure thecurrent through the sensor.
 10. The test and measurement instrument ofclaim 9, wherein the measurement device is further configured to measurea voltage of the device under test simultaneously with measuring thecurrent through the sensor, wherein the measured current through thesensor substantially represents the current in the device under test.11. A method for characterizing a device under test, comprising:charging a capacitor by a direct current voltage source; generating apulse by a pulse generator for testing the device under test; andmeasuring a current through the device under test based on the pulse.12. The method of claim 11, wherein the capacitor discharges when thepulse is received at the device under test and the method furtherincludes measuring the current through the device under test as thecapacitor discharges.
 13. The method of claim 11, wherein the pulse isgenerated at a predetermined voltage.
 14. The method of claim 11,wherein the direct current voltage source charges the capacitor to apredetermined level based on the device under test.
 15. The method ofclaim 11, further comprising receiving the pulse at a control terminalof the device under test.
 16. The method of claim 11, further comprisingreceiving the pulse from the pulse generator at a switch to dischargethe capacitor.
 17. The method of claim 16, wherein the pulse is receivedat a control terminal of the switch.
 18. The method of claim 11, whereinthe current is measured using a resistor in series with the device undertest.
 19. The method of claim 18, wherein the current is measuredthrough the resistor as the capacitor discharges.
 20. The method ofclaim 19, further comprising measuring a voltage of the device undertest simultaneously with measuring the current.